1. Field of the Invention
The present invention generally relates to power converters; more specifically, the present invention relates to quasi-resonant power converters.
2. Description of the Related Art
To achieve higher efficiency and reduce power loss of a power converter under high switching frequency, quasi-resonant (QR) technique is widely applied. However, one drawback of the QR power converter is lower efficiency under light-load condition. The switching frequency of QR power converter is varied in response to an input voltage and an output load of the QR power converter. Its switching frequency is normally increased when the output load is decreased. Acoustic noise might be generated during the valley switching operation, which becomes a main issue to be resolved.
The operative description of QR power converter can be found in the prior art:
“Switching Control Circuit Having a Valley Voltage Detector to Achieve Soft Switching for a Resonant Power Converter”, U.S. Pat. No. 7,426,120.